Method for manufacture of a solar cell

ABSTRACT

The invention relates to a method for manufacture of a semiconductor component by the formation of a hydrogenous layer containing silicon on a substrate comprising or containing silicon such as a wafer or film. In order to achieve a good surface and volume passivation, it is proposed that during formation of the siliceous layer in the form of SiN x O y  with 0&lt;x≦1.5 and 0≦y≦2 one or more catalytically acting dopants are selectively added into the layer which release hydrogen from the SiN x O y  layer. The concentration C of the dopants is 1×10 14  cm 3 ≦C≦10 21  cm 3 .

[0001] The invention relates to a method for manufacture of a solar cellby the formation of a hydrogenous layer containing silicon in the formof a passivation and/or anti-reflexion layer on a substrate comprisingor containing silicon such as a wafer or film.

[0002] More than 80% of all solar cells are currently made fromcrystalline silicon wafers manufactured either using the Czochralskimethod or by means of block casting. A silicon mass in the form of around column or large block is here crystallized and then sawn intoindividual wafers. This high proportion will presumably increasemarkedly in the coming years on account of new production capacities,since many manufacturers prefer the production techniques tried andtested for many years and based on crystalline silicon wafers to the newtechnologies.

[0003] Thin-film solar cells are currently being discussed as futurealternatives to solar cells of silicon wafers (typical thickness around300 μm); in comparison with solar cells made of crystalline siliconwafers, they make do with considerably less semiconductor material(thickness approx. 1-10 μm). These cells can be deposited using avariety of methods directly onto large glass surfaces and therefore holdout the promise of considerable potential cost reductions. Amorphoussilicon thin-film solar cells with efficiencies in the 6 to 8% range arealready commercially available. Higher efficiencies can be achieved withcomposite semiconductors such as CdTe or CuInS₂. Solar cells made fromthese materials are currently being tested in pilot production lines (A.Abken et al., Proc. 16 EPVSEC, 2000; D. Cunningham et al., Proc. 16thEPVSEC, 2000). Whether these materials will make headway in the longterm is not at present clear, as some of them are toxic or are availableonly in small quantities. There are high hopes for material-savingcrystalline Si thin-film solar cells, since silicon is environmentallycompatible and has unlimited availability. These cells are however stillat a very early stage (R. Brendel et al., Proc. 14th EPVSEC, p 1354,1997; K. Feldrapp et al., Proc. 16th EPVSEC, 2000).

[0004] A second alternative to conventional manufacture of solar cellsfrom crystalline silicon wafers is the use of silicon films. Heresilicon is directly crystallized as a film in the thickness necessaryfor solar cells. This avoids the considerable cutting losses entailed bythe classic block casting or Czochralski methods. The Edge-definedFilm-fed Growth (EFG) method is already in industrial use, andpermitting the manufacture of very high-quality silicon films. Thelatest developments are aimed at the reduction of the film thickness toapprox. 100 μm. Unlike the block casting or Czochralski methods, thefilm method permits a marked reduction in the manufacturing costs, sincethe ratio of cutting losses to wafer volume does not increase here asthe wafers become thinner. For that reason, silicon films could dominatethe market during the long-term transition from the present wafertechnology to thin-film technology.

[0005] A central factor in all silicon solar cells is the effective lifeof the charge carriers generated by light in the crystal volume. Thismust be sufficient to permit all charge carriers to diffuse to the metalcontacts if possible and hence reach the connected circuit. This appliesto the currently dominant block-cast and Czochralski-type wafers, to thesilicon films which will presumably find greater application in themedium term, and to the crystalline silicon thin-film solar cells whichmight be possible in the future.

[0006] The effective charge carrier life of crystalline silicon islimited by crystal defects (offsets or flaws), by crystal impurities(including metal atoms), and by the quality of the crystal surface (e.g.dangling bonds). A sufficient avoidance of crystal defects andimpurities and the manufacture of an ideal surface even during thecrystal and wafer manufacture is not possible due to technologicalobstacles or for economic reasons. Attempts are therefore being made inthe downstream solar cell manufacturing processes to improve theoriginally often short charge carrier life of the silicon wafers.

[0007] This is possible by a subsequent reduction of the impurities(Gettern) (L. J. Caballero et al., Proc. 16th EPVSEC 2000), byelectronic “alleviation” of crystal defects by adding atomic hydrogeninto the crystal (hydrogen volume passivation) (B. L. Sopori et al.,Solar En. Mat. & Solar Cells 41/42, p. 159, 1996), and by depositingsurface coatings to prevent charge carrier combination on the surface(electronic surface passivation) (A. Aberle, R. Hezol, Progr. in PV 5,p. 29, 1997).

[0008] Processes in this respect can be of crucial importance for goodsolar cell efficiencies and are therefore already in use by industry invarious designs.

[0009] For hydrogen volume passivation of silicon solar cells, knownmethods include the hydrogen plasma, tempering in forming gas anddiffusion of hydrogen from a hydrogenous silicon nitride surface layer(SiN). For electronic surface passivation the known methods includeoxidation of the silicon surface (S. Wenham et al., Solar En. Mat. &Solar Cells 65, p. 377, 2001) and application of a hydrogenous siliconnitride surface layer (A. Aberle, R. Bezel, Progr. in PV 5, p. 29,1997). Of all the known methods, the application of a hydrogenous SiNsurface layer is the only one that can achieve both processes at thesame time. For this reason, more and more solar cell manufacturers areusing SiN layers in their production. A further advantage of SiN surfacecoatings is that they have in addition to their passivation propertiesexcellent optical parameters, allowing them to be used as effectiveanti-reflexion coatings.

[0010] Hydrogen volume passivation with the aid of a SiN surface coatingtakes place in two process steps; first the hydrogenous SiN layer isapplied to the surface of the silicon wafer. In so doing, a smallproportion of atomic hydrogen can already penetrate into a surface-neararea of the silicon wafer. This is followed by a high-temperaturetreatment at temperatures in excess of 700° C. At these hightemperatures, a relatively large amount of atomic hydrogen in thesurface layer is freed and diffuses deep into the silicon crystal (B. L.Sopori et al., Solar En. Mat. & Solar Cells 41/42, p. 159, 1996; J.Jeong et al., J. Appl. Phys. 87 (10), p. 7551, 2000). The electronicsurface passivation with the aid of a SiN surface coating is achieved bytwo effects. Firstly, the hydrogen contained in the layer collects atthe silicon surface and passivates dangling silicon bonds, such thatthese become electronically ineffective. Secondly, fixed insulatorcharges are created in the layer, which by their influence generate inthe silicon an electrical field which leads to a strengthening of theelectronic passivation effect (charge carriers are kept away from thesurface and hence cannot be lost) (A. G. Aberle et al., Solar En. Mat. &Solar Cells 29, p. 175, 1993). The manufacturing methods of SiN surfacecoatings known for solar cell applications are;

[0011] a) Parallel-Plate Plasma:

[0012] In this method, process gases containing silicon and nitrogen,preferably silane and ammonia, are excited in a low pressure system by aplasma discharge and brought to a reaction. The plasma discharge isgenerated between two parallel plates by applying an A.C. voltage. Thisis typically in the kHz or MHz frequency range, with a voltage of 100 to1000 V (R. Reif in: Handbook of Plasma Processing Technology, Noycs,N.J., 1990, p. 269 ff.).

[0013] b) Remote Microwave Plasma:

[0014] Ammonia and nitrogen is excited in a low pressure plasma outsideor in a separate area of the coating chamber and then passed to thesubstrate. On the way there, a siliceous process gas (as a rule silane)is admixed. The excited nitrogenous gas reacts with the siliceous gas,leading to a layer deposition on the substrate.

[0015] c) LPCVD

[0016] Nitrogenous and siliceous process gases are brought thermally toa reaction in a low pressure system at temperatures in excess of 700° C.In view of the high temperatures required, this method involves severaldrawbacks; these include the fact that temperature-sensitive substratescannot be processed and the hydrogen content of the SiN layers is low,as at these temperatures the major part of the hydrogen effuses from thelayer.

[0017] For the surface coating of solar cells for hydrogen volumepassivation and electronic surface passivation with SiN, parallel-plateSiN and remote, microwave SiN layers have been exclusively used to date(A. G. Aberle, Solar En. Mat. & Solar Cells 65, p 239, 2001). Bothmethods have the drawbacks that the effectiveness of the SiN layers isdependent to a high degree on the layer composition and on thedeposition parameters (T. Lauinger et al., J. Vac. Sci. Technol. A16(2), p. 530, 1998). This creates the following problems:

[0018] insufficiently high solar cell efficiencies, since the layersused do not exploit the full potential for hydrogen volume passivationand electronic surface passivation,

[0019] during the process introduction, expensive optimizationexperiments are necessary to ascertain the possible parameter windows;

[0020] in operation, expensive process checks are necessary to permit aconstant quality of the layers;

[0021] the narrow parameter windows in which good volume passivation ispossible restrict the variation possibilities of layer manufacture, sothat the layers cannot be simultaneously optimized in respect of theiranti-reflexion and surface passivation qualities;

[0022] the economic potential cannot be exploited to the full because ofthe overall sensitive method and the high checking effort involved.

[0023] A method for nitridation of silicon surfaces of semiconductorelements (ULSI) is known from Appl. Phys Lett. 71(10), p. 1371, Izumi,Matsumara, “Low-temperature nitridation of silicon surfaceNH₃-decomposed species in a catalytic chemical vapor deposition system”.SiN_(x)O_(y) layers have a stoichiometry ratio of Si:N:O=1:0.9:0.3 witha maximum thickness of 4.8 nm. The layer is manufactured using theCat-CVD method with tungsten wire as the catalyst. Measurements haveshown that impurities in the SiN_(x)O_(y) layer resulting from tungstenare negligible. Use of a corresponding nitridation for solar cells isunsuitable in view of the low layer thickness of the SiN_(x)O_(y).

[0024] To form photovoltaically active layers for a solar cell, poly-Sican be deposited using the Cat-CVD method (Solar Energy Materials &Solar Cells 69 (2001) 107-114, Niira et al., “Thin film poly-Siformation for solar cells by Flux method and Cat-CVD method”). In thepoly-Si layers, metal impurities occur in a concentration of 2×10¹⁴ cm³to 2×10¹⁸ cm³.

[0025] In Solar Energy Materials & Solar Cells Vol. 65, p. 541-547,Schiopp et al., “Polysilicon films with low impurity concentration madeby hot wire chemical vapour deposition”, it is described how poly-Si isdeposited by means of HWCVD. Impurities of tungsten in a concentrationof 10¹⁶ cm³ could be ascertained.

[0026] A method for catalytic deposition of a passivation layer on asemiconductor substrate is known from U.S. Pat. No. 6,225,241 B1.

[0027] The problem underlying the present invention is to develop amethod for manufacture of a solar cell such that besides good opticalproperties both a good surface passivation and a good volume passivationof the substrate are possible. An economical manufacture should bepossible with good reproducibility. In particular, a good volumepassivation should be feasible with large parameter windows, to obtainat the same time the required anti-reflexion and surface passivationlayers.

[0028] The problem is solved in accordance with the inventionsubstantially in that during formation of the siliceous layer in theform of SiN_(x)O_(y) with 0<x≦1.5 and 0≦y≦2 one or more catalyticallyacting dopants with a concentration C of 1×10¹⁴ cm⁻³≦C≦10²¹ cm⁻³ areselectively added into the layer. The dopants release hydrogen from theSiN_(x)O_(y) layer and/or influence the structure of the layer such thatthe latter can emit more hydrogen. In particular, the SiN_(x)O_(y) layeris formed with mean values over its layer thickness of 0.1≦x≦1.5 and0.01<y<2.

[0029] The concentration C should preferably be between 10¹⁶ cm⁻³≦C≦10¹⁹cm⁻³.

[0030] In a particularly noteworthy manner, the dopant(s) is/aresubstances made of or containing Groups V and V1 of the periodic systemor the group of refractory metals. The preferred dopants are heremolybdenum tantalum, tungsten, platinum and/or rhenium.

[0031] Here elementary tungsten and/or WO_(x) with 0≦x≦4 can beemphasized in particular as a dopant, having a particularly favorableinfluence on the structure of the growing SiN_(x)O_(y) layer thanks tonucleation and effecting catalytically the activation of hydrogencontained in the layer so that both a volume passivation and a surfacepassivation of the substrate made up of or containing silicon areperformed to the required extent.

[0032] In accordance with the invention, a hydrogenous SiN_(x)O_(y)layer is selected that releases hydrogen during growth and tempering.The layer is provided with one or more dopants that, as a catalystduring growth of the layer, lead to an improved structural incorporationof hydrogen, to a separation of atomic hydrogen (protons) fromhydrogenous molecules or from molecular hydrogen, or during tempering ofthe layer to a separation of atomic hydrogen from the atomic union ofthe layer.

[0033] Parallel to the surface passivation or volume passivation, ananti-reflexion layer is formed during the surface coating of thesubstrate of the solar cell.

[0034] Diverging from the previously prevalent view, during theformation of a SiN_(x)O_(y) layer of a solar cell in particular metallicdopants are selectively added that were otherwise rated as contaminationand that lead in the manufacture of semiconductor components to adeterioration in quality. Surprisingly, the result on the basis of theteachings in accordance with the invention, i.e. the selective adding inof dopants comprising in particular one or more refractory metals, is animprovement of the solar cell properties, both by volume passivation andby surface passivation with hydrogen. It has become clear here that asimple process check is possible without having to allow fordeteriorations in respect of reproducibility or quality.

[0035] A further advantage resulting is wide parameter windows in whicha good surface passivation and volume passivation is possible, so thatvariation possibilities in layer manufacture are not restricted andhence a simultaneous optimization of the layers in respect of theiranti-reflexion and surface passivation qualities is possible.

[0036] The effectiveness of the doping by the dopant(s) can beinfluenced by the structure and thickness of the hydrogenous siliconnitride layer and/or gradients of the doping concentration of thedopant(s) over the layer thickness.

[0037] In the case of homogeneously formed SiN_(x)O_(y) layers, thestoichiometry x should be between 0.1 and 1.5 for layer thicknesses inthe range between 50 nm and 110 nm.

[0038] Making the homogeneous surface layer often however createsproblems, as structural changes in the surface layer often result fromthe influence of the substrate surface, in particular at the junctionbetween the substrate and the surface layer. For that reason, anembodiment of the invention provides that a selective change of thestoichiometry of the SiN_(x)O_(y) layer takes place such that x variesbetween 0.1 and 1.5 and/or y varies between 0 and 2.0 over the layerthickness, preferably with x increasing with the layer thickness in therange between 0.6 and 1.3 and y in the range between 0.1 and 1.0.

[0039] If as already mentioned the doping of the dopants is selected soas to be homogeneous, a gradient formation over the layer thickness isalso possible, in particular with the concentration of the dopantsincreasing in the range 1×10¹⁵ cm⁻³ to 1×10¹⁸ cm⁻³ as the layerthickness increases.

[0040] One advantage of the selective formation of surface layers withsteep gradients and variable thickness is an improved anti-reflexionproperly of the silicon nitride layer.

[0041] The teachings in accordance with the invention can be realizedfor all types of surface layer, i.e. with or without gradients and withdifferent thicknesses. As already mentioned, it is also possible tomanufacture the doping concentration with a gradient over the layerthickness, permitting adaptation to various surface layer systems.

[0042] A possible method for doping of SiN_(x)O_(y) layers withrefractory metals is the method using catalytic deposition of siliconnitride by the excitation of hydrogenous silicon and nitrogen compoundssuch as silane, disilane, ammonia, hydrogen or hydrazine gases in lowpressure systems on hot refractory metals in the form of flat sheets orwires such as tantalum, molybdenum, tungsten, rhenium, platinum and/orniobium.

[0043] The use of suitable methods for the deposition of diamond layersis known, as are processes for the deposition of amorphous silicon forsolar cells and processes for the deposition of silicon nitride aschemical/mechanical passivation, i.e. protection layer for integratedsemiconductor components; however care was taken during the formation ofappropriate protective layers to ensure that contamination by metals wasruled out, as otherwise the quality of the semiconductor component wouldsuffer (H. Matsumura, Jpn. J. Appl. Phys. 37, p. 3175, 1998).

[0044] In particular, the invention provides for deposition ofhydrogenous and doped surface layers on large-area silicon substrates.Here the large-area silicon substrate can be deposited as a thin siliconlayer on a carrier material. The carrier material can be a glass sheet,a ceramic plate, a metal sheet or a polymer film. The silicon substrateitself can have a micro-crystalline, amorphous or multi-crystallinecrystal structure.

[0045] It is furthermore possible to form the large-area siliconsubstrate from a mono-crystalline or multi-crystalline silicon layer orfrom a silicon film. In particular, a silicon film manufacturedaccording to the EFG method (Edge-defined Film-fed Growth) can be used.Regardless of this, the large-area silicon substrate can have a p-njunction.

[0046] By setting of coating parameters such as pressure, temperature ofdopant metal, gas composition, oxygen partial pressure, substratetemperature, distance between metal and substrate, and metal geometry, arequired doping of the SiN_(x)O_(y) layer with the dopant such as inparticular a refractory metal is possible. In particular, the depositionparameters should be within the following ranges: Pressure P: 0.1 Pa ≦ P≦ 1000 Pa Metal temperature T: 1500° C. ≦ T ≦ 2500° C. Gas composition(ratio of siliceous 0.001-1.0 to nitrogenous reaction gases): Oxygenpartial pressure: 0-20 Pa Substrate temperature: 20° C.-600° C. Distancemetal to substrate: 1-100 mm Geometry of metal: Rod, wire or plate.

[0047] To form the SiN_(x)O_(y) layer with selective doping of thedopants, a continuous or a static operation can take place. The firstmeans that the substrate is added into the coating area when the coatingsource, comprising hot metal and the gas supply and removal, is switchedoff, with the layer being formed with the substrate stationary.Alternatively, it is possible to coat in cycles, meaning that with thecoating source operating substrates are placed into the coating area,coated there, and then removed again. Finally, a continuous throughputprocess is possible in which the substrates are placed continuously intothe coating area, passed through the latter, and removed from it.

[0048] In particular, a change of the stoichiometry in the layercomposition of silicon nitride can occur due to a change in theparameters gas composition, pressure, metal temperature and total gasflow, the stoichiometry varying between 0.1 and 1.5. A change of thestoichiometry in the layer composition over the layer thickness is alsopossible by a time change in the parameters gas composition, pressure,metal temperature and total gas flow during a static coating. Aselective stoichiometry setting is also possible by a spatial change ofthe parameters gas composition, pressure, metal temperature, metalgeometry and total gas flow along the coating distance. The compositionof the process gases without flow rate (closed chamber deposition) canbe achieved using the reaction speed of the deposition.

[0049] The advantages achievable thanks to the teachings in accordancewith the invention are made clear by the following table. For example,during the manufacture of EFG solar cells with hydrogenous SiN_(x)O_(y)surface layers, a surprising correlation was found of the solar cellefficiency (Eta) with the content of tungsten as a dopant in theSiN_(x)O_(y) layer. Si N 0 H Fe W Eta Group [At %] [At %] [At %] [At %][At %] [At %] [%] 1 37 47 1.1 15 — — 13.34 2 37 51 1.1 12 — — 13.45 3 3750 1.8 11 0.008 — 13.50 4 37 48 1.6 13 0.007 0.020 14.04 5 36 50 2.1 120.002 — 13.38

[0050] As the table shows, all groups have comparable silicon, nitrogenand hydrogen concentrations. Significant variations can be observed inthe oxygen, iron and tungsten concentrations. Both an increased oxygen(Group 5) and an increased iron concentration (Group 3) in the SiNlayers lead to no improvement in the solar cell efficiency compared withreference groups with low impurity contents (Groups 1 and 2). All thesegroups have efficiencies between 13.34 and 13.50%. By contrast, theincreased tungsten concentration shown in Group 4 correlates clearlywith a 14.04% efficiency, absolutely increased by 0.6%, of the solarcells.

[0051] While the result for Group 4 is a tungsten concentration ofapprox. 10¹⁹ cm⁻³, it should be noted that an effect occurs even at verymuch lower concentrations, since hydrogen can diffuse very well andhence a few foreign atoms lead to a large number of active hydrogenatoms. A lower limit of effectiveness for foreign substance dopingshould be in the order of magnitude of 10¹⁴ cm⁻³.

[0052] The causes for the better efficiencies of solar cells withW-doped SiN_(x)O_(y) layer may lie in three mechanisms. Firstly, thetungsten atoms can act as a catalyst during manufacture of the layersand hence have a positive effect on the growth reactions in progress(for example it is conceivable that in the presence of tungsten a higherconcentration of atomic hydrogen occurs due to the splitting ofmolecular hydrogen, N—H bonds or Si—H bonds. This can in particular leadto an improved electronic surface passivation).

[0053] Secondly, the tungsten atoms can lead during the downstreamhigh-temperature treatment, again acting as a catalyst, to an increasedconcentration of atomic hydrogen due to the splitting of molecularhydrogen, N—H bonds or Si—H bonds, and thereby assist in particular thehydrogen volume passivation.

[0054] Thirdly, tungsten atoms can during layer growth lead to anucleation of crystalline silicon nitride and hence to a positivestructural change of the entire layer.

[0055] As a result of the tungsten doping in the hydrogenous surfacecoating, hydrogen is additionally activated for volume passivation andsurface passivation. Instead of tungsten, all refractory metals inparticular with similar chemical properties can also be used, such asMo, Ta, Pt or Re. Furthermore, all foreign atoms or foreign moleculeswhich like tungsten lead to an additional activation of hydrogen aresuitable. Carbon can be mentioned in particular as an example. Foreignatoms in the meaning of the invention and effecting surface and volumepassivation do not however include oxygen and hydrogen.

[0056] To manufacture solar cells, the doped hydrogenous surface layersmust be deposited over a wide area onto the silicon substrates whichdiffer depending on the solar cell type. To do so, the parallel-platetechnology available on an industrial scale can be employed, if suitablegas additives are used that lead to deposition of the required foreignatoms in the applied layers. Since these coating methods have alreadybeen developed for widely differing substrate types, the deposition ofthe doped layers onto all these substrate types is possible, and hencealso onto solar cells made from thin silicon layers using these carriermaterials. The possible carrier materials are glass sheets, ceramicplates, metal sheets or polymer films. With substrate-independentcoating methods such as remote microwave plasma or LPCVD technology,doped hydrogenous layers can in principle be deposited onto all types ofsubstrate.

[0057] The teachings in accordance with the invention are hence suitablefor all types of large-area semiconductor components, in particularhowever of silicon solar cells with micro-crystalline, amorphous ormulti-crystalline crystal structure in the form of films (e.g. EFG),wafers or thin layers on a carrier material. In particular, they aresuitable for the passivation of large-area p-n junctions.

[0058] The invention is explained in greater detail in the following onthe basis of embodiments:

EXAMPLE 1

[0059] The starting material is a 100×100 mm boron-doped silicon waferof 300 μm thickness with a conductivity of approx. 5 Ωcm and one-sidedphosphorus diffusion with an emitter layer resistance of approx. 40Ω/sq.

[0060] This wafer is moved into a vacuum chamber and heated at apressure of less than 5×10⁻³ mbar to 300° C. The wafer lies in thevacuum chamber on a horizontal special steel plate equipped with heaterspirals. About 100 mm above the wafer is a quartz glass pipe passingvertically through the wall of the vacuum chamber and with a diameter of20 mm.

[0061] After heating up of the wafer, ammonia is introduced into thechamber via the quartz glass pipe. Around 20 mm to the side of thequartz pipe is a further gas inlet through which silane is introducedinto the chamber via a distributor nozzle. The mixing ratio of the gasesis 1:2 (silane:ammonia). The pressure in the chamber is controlled usinga setting valve in the gas outlet to 3×10⁻² mbar.

[0062] The quartz glass pipe is surrounded outside the vacuum chamber bya microwave resonator, in which 120 W of microwave power (frequency 2.54GHz) is connected, as a result of which an ammonia plasma forms insidethe glass pipe. Directly at the outlet of the quartz glass pipe is aplatinum spiral which is heated to approx. 1900° C. and flowed over bythe ammonia excited in the quartz glass pipe.

[0063] The excited ammonia reacts with the silane to form siliconnitride, which is deposited into the silicon wafer. Platinum atomsevaporate from the heated platinum coil and are incorporated into thesilicon layer, thus leading to doping of the layer in accordance withthe invention. The coating process is performed until a thickness of thesilicon nitride layer of 75 nm is achieved.

[0064] Further processing of the wafers coated in this way to form solarcells leads to efficiencies greater than 14.5%.

EXAMPLE 2

[0065] The starting material is a 100×100 mm boron-doped silicon waferof 300 μm thickness with a conductivity of approx. 5 Ωcm and one-sidedphosphorus diffusion with an emitter layer resistance of approx. 40Ω/sq.

[0066] This wafer is moved into a vacuum chamber and heated at apressure of less than 5×10⁻³ mbar to 300° C. The wafer lies in thevacuum chamber on a horizontal and circular special steel plate equippedwith heater spirals and having a diameter of 300 mm. About 20 mm abovethe wafer is circular special steel plate with a diameter of 300 mmcontaining evenly distributed gas outlet openings with a diameter of 0.5mm.

[0067] After heating up of the silicon wafer, ammonia, silane andmethane are introduced via the upper special steel plate. The mixingratio of the gases is 1:2:0.001 (silane:ammonia:methane). The pressurein the chamber is controlled using a setting valve in the gas outlet to5×10⁻² mbar.

[0068] An A.C. voltage of 700 V (frequency 100 kHz) is applied betweenthe upper and lower special steel plates, so that plasma is formedbetween the two plates.

[0069] The excited ammonia reacts with the silane to form siliconnitride, which is deposited into the silicon wafer. The methanemolecules react with the plasma radicals such that carbon isincorporated into the silicon layer, thus leading to doping of the layerin accordance with the invention. The coating process is performed untila thickness of the silicon nitride layer of 75 nm is achieved.

[0070] Further processing of the wafers coated in this way to form solarcells leads to efficiencies greater than 14.6%.

1. A method for manufacture of a solar cell by the formation of ahydrogenous layer containing silicon in the form of a passivation and/oranti-reflexion layer on a substrate comprising or containing siliconsuch as a wafer or film, wherein during formation of the siliceous layerin the form of SiN_(x)O_(y) with 0<x≦1.5 and 0≦y≦2 one or morecatalytically acting dopants with a concentration C of 1×10¹⁴cm⁻³≦C≦10²¹ cm⁻³ are selectively added into the layer.
 2. Methodaccording to claim 1, wherein the SiN_(x)O_(y) layer is formed with meanvalues over its layer thickness of 0.1<x<1.5 and 0.01<y<2.
 3. Methodaccording to claim 1, wherein the dopant(s) is/are added in with aconcentration C of 1×10¹⁶ cm⁻³≦C≦1×10¹⁹ cm³.
 4. Method according toclaim 1, wherein the dopant or dopants are added in with a gradient overthe thickness of the SiN_(x)O_(y) layer, with the concentration C of thedopant(s) in particular increasing with increasing layer thickness inthe range between 1×10¹⁴ cm⁻³ and 1×10¹⁹ cm⁻³.
 5. Method according toclaim 1, wherein the dopant or dopants is/are added in a homogeneousdistribution into the SiN_(x)O_(y) layer.
 6. Method according to claim1, wherein atoms from the range of refractory metals or containing thesearc used as the dopant or dopants.
 7. Method according to claim 1,wherein molybdenum, tantalum, tungsten, platinum, rhenium or carbon orcompounds thereof are used as the dopant.
 8. Method according to claim1, wherein the substrate is deposited on a glass sheet, a ceramic plate,a metal sheet or a polymer film.
 9. Method according to claim 1, whereinthe substrate comprising silicon has a micro-crystalline, amorphous ormulti-crystalline crystal structure.
 10. Method according to claim 1,wherein the substrate comprises a mono-crystalline or multi-crystallinesilicon wafer or a silicon film.
 11. Method according to claim 10,wherein a film manufactured according to the EFG method (Edge-definedFilm-fed Growth) is used as the silicon film.
 12. Method according toclaim 1 wherein elementary tungsten and/or WO_(x) with 0≦x≦3 is used asthe dopant.
 13. Method according to claim 1, wherein the dopant used isone which for formation of the SiN_(x)O_(y) layer catalyticallydecomposes gases used such as silane, disilane, hydrogen, ammonia orhydrazine.
 14. Method according to claim 1, wherein the hydrogenousSiN_(x)O_(y) layer comprises amorphous hydrogenized silicon nitride. 15.Method according to claim 1, wherein the SiN_(x)O_(y) layer ishomogeneously formed.
 16. Method according to claim 1, wherein theSiN_(x)O_(y) layer varies over its thickness, with x increasing with thelayer thickness in the range between 0.6 and 1.3 and y in the rangebetween 0.1 and 1.0.
 17. Method according to claim 1, wherein theSiN_(x)O_(y) layer is formed such that its thickness is in the rangebetween 30 nm and 150 nm, in particular in the range between 50 nm and110 nm.
 18. Method according to claim 1, wherein the hydrogenousSiN_(x)O_(y) layer is formed by the excitation of gaseous andhydrogenous silicon and nitrogen compounds, preferably silane, disilane,ammonia hydrogen or hydrazine on hot refractory metals.
 19. Methodaccording to claim 1, wherein the SiN_(x)O_(y) layer is formed in areaction room in which a pressure P of 0.1 Pa≦P≦1000 Pa prevails. 20.Method according to claim 19, wherein the pressure P in the reactionroom is set to 1 Pa≦P≦200 Pa.
 21. Method according to claim 1, whereinthe thickness of the hydrogenous SiN_(x)O_(y) layer is set by coatingparameters such as pressure, metal temperature, gas composition, oxygenpartial pressure, substrate temperature, distance between metal andsubstrate, and/or metal geometry.
 22. Method according to claim 1,wherein the metal forming the dopant or dopants is set to a temperaturebetween 1500° C. and 2500° C.
 23. Method according to claim 21, whereinthe gas composition is set such that the ratio between siliceous andnitrogenous reaction gas is 0.001 to 1.0.
 24. Method according to claim21, wherein the oxygen partial pressure is set to a value p with 0<p≦20Pa.
 25. Method according to claim 21, wherein the substrate is set to atemperature between 20° C. and 600° C.
 26. Method according to claim 21,wherein the distance between the metal and the substrate is set tobetween 1 mm and 100 mm.
 27. Method according to claim 21, wherein themetal used is one having the geometry of a rod, wire and/or a plate. 28.Method according to claim 1, wherein the hydrogenous SiN_(x)O_(y) layeris formed in a static coating operation.
 29. Method according to claim1, wherein the hydrogenous SiN_(x)O_(y) layer is formed in a cycliccoating operation on the substrate.
 30. Method according to claim 1,wherein the SiN_(x)O_(y) layer is formed on the substrate in acontinuous throughput coating operation.
 31. Method according to claim21, wherein the composition of the process gases without flow rate isset using the reaction speed of the deposition.
 32. Method according toclaim 1, wherein the stoichiometry composition or the SiN_(x)O_(y) layeris set by changing the parameters gas composition, pressure, metaltemperature and/or total gas flow.
 33. Method according to claim 28,wherein the stoichiometry change in the layer composition of theSiN_(x)O_(y) layer over its thickness is set by a time change in theparameters gas composition, pressure, metal temperature and/or total gasflow during the static coating operation.
 34. Method according to claim16, wherein the stoichiometry change in the layer composition of theSiN_(x)O_(y) layer over the layer thickness is set by a spatial changeof the parameters gas composition, pressure, metal temperature, metalgeometry and/or total gas flow along the coating distance.